1. Field of the Invention
The present invention relates to a thin film magnetic head comprising at least an inductive magnetic transducer for recording, and a magnetic recording apparatus comprising the thin film magnetic head.
2. Description of the Related Art
In recent years, an improvement in performance of a thin film magnetic head has been sought in accordance with an increase in the areal density of a magnetic recording medium (hereinafter simply referred to as “recording medium”) such as a hard disk. As recording systems of the thin film magnetic head, for example, a longitudinal recording system in which a signal magnetic field is oriented in an in-plane direction (a longitudinal direction) of a recoding medium and a perpendicular recording system in which the signal magnetic field is oriented in a direction perpendicular to a surface of the recording medium are well known. At present, the longitudinal recording system is widely used, but in consideration of market forces in accordance with an improvement in areal density, it is assumed that the perpendicular recording system instead of the longitudinal recording system holds promise for the future, because the perpendicular recording system can obtain advantages that higher linear recording density can be achieved and that a recording medium in which data has been already recorded has resistance to thermal decay effects.
A main part of the perpendicular recording system thin film magnetic head comprises, for example, a thin film coil generating a magnetic flux, a pole layer emitting the magnetic flux generated in the thin film coil to outside to execute a recording process, and a return yoke layer (return pole layer) returning the magnetic flux which is emitted from the pole layer to magnetize a recording medium. As the thin film magnetic head of this kind, for example, some thin film magnetic heads in which the return yoke layer is disposed on a trailing side (a medium-outgoing side) of the pole layer are known (refer to U.S. Pat. No. 4,656,546, Japanese Patent Application Publication No. Hei 05-325137 and Japanese Patent Application Publication No. Hei 06-236526, for example). In these thin film magnetic heads, when the magnetic flux is emitted from the pole layer, a component expanding to the surroundings in the magnetic flux emitted from around an edge of the pole layer on the trailing side flows into the return yoke layer, and as a result, the expansion of the magnetic flux can be prevented. Therefore, compared to a thin film magnetic head comprising no return yoke layer, a gradient of a recording magnetic field in proximity to a recording-medium-facing surface (air bearing surface) becomes steep, so as a result, the thin film magnetic head comprising the return yoke layer can obtain an advantage that a SN (Signal to Noise) ratio can be improved.
In order to put the perpendicular recording system thin film magnetic head into widespread use, it is required to stably secure recording characteristics. However, in a conventional thin film magnetic head in which the return yoke layer is disposed on the trailing side of the pole layer, the SN ratio is improved according to the presence of the return yoke layer, but when the return yoke layer is too close to the pole layer, most of the magnetic flux emitted from the pole layer directly flows into the return yoke layer without reaching the recording medium, so consequently, recording magnetic field strength declines, thereby overwrite characteristics may decline. Therefore, in the thin film magnetic head comprising the return yoke layer on the trailing side of the pole layer, it is desired to establish a technique for making possible to secure the recording characteristics.